Problem: $ B = \left[\begin{array}{rrr}1 & 2 & 1 \\ 2 & 0 & 1 \\ 1 & 0 & 0\end{array}\right]$ What is $ B^{-1}$ ?
$ = \left[\begin{array}{rrr}0 & 0 & 1 \\ \frac{1}{2} & -\frac{1}{2} & \frac{1}{2} \\ 0 & 1 & -2\end{array}\right]$